We report the self-assembly of 2D double perovskite (BLA) 2 CsAgBiBr 7 (BLA = benzylammonium) on 3D Cs 2 AgBiBr 6 crystals, providing the first demonstration of polarization-sensitive photodetection using lead-free double perovskite heterocrystals (HCs). The (BLA) 2 CsAgBiBr 7 /Cs 2 AgBiBr 6 HC successfully combines the anisotropy of 2D double perovskites with the well-defined interface provided by heterogeneous integration. Driven by the built-in electric field in junction, photodetectors of HCs exhibit unique polarization dependence of zero-bias photocurrent with a large anisotropy ratio up to 9, which is 6 times amplified as compared to the pristine 2D (BLA) 2 CsAgBiBr 7 . More importantly, the present devices can remain polarization-sensitive with incident light intensity down to the nW cm À 2 level. Our study on lead-free hybrid perovskite HCs marks a step toward establishing robust material foundations for fundamental scientific investigations and the development of optoelectronic devices.
Chiral metal halide perovskites (CMHPs) have recently shown great potential for direct circularly polarized light (CPL) detection. However, owing to the limited cutoff wavelength edge of these CMHPs, most of the detectors presented thus far are characterized only in the ultraviolet and visible range; CMHPs that target at the near-infrared (NIR) region are still greatly desired. Here, we design a novel CMHP heterostructure, synthesized via solution-processed epitaxial growth of crystalline 3D MAPbI3 on a 2D chiral (R-BPEA)2PbI4 (R-BPEA = (R)-1-(4-bromophenyl)ethylammonium) crystal, and provide the first demonstration of self-powered direct NIR-CPL detection. Compared with individual chiral (R-BPEA)2PbI4, the heterostructure not only retains the spin selectivity but also allows much broader absorbance, especially beyond 780 nm, where the (R-BPEA)2PbI4 cannot absorb. Furthermore, the built-in electric potential in the heterojunction forces spontaneous separation/transport of photogenerated carriers, enabling the fabrication of devices operating without external energy supply. By making use of the abovementioned advantages, the self-powered CPL detectors of the (R-BPEA)2PbI4/MAPbI3 heterostructures hence show competitive circular polarization sensitivity at 785 nm with a high anisotropy factor of up to 0.25. In addition, a large on/off switching ratio of ∼105 and an impressive detectivity of ∼1010 Jones are also achieved. As a pioneer study, our results may broaden the material scope for future chiroptical devices based on CMHPs.
So far, materials preparing for UV photodetectors with low detection limit can be a variety of materials other than silicon-based such as ZnO, [4] GaN, [5] and SiC [6] in the form of single crystals, thin films, quantum dots, nanowires, and heterostructure. For instance, Tang et al. based on n-Ga 2 O 3 /p-CuSCN (under 1.5 µW cm −2 at 254 nm) [3a] and Yao et al. based on Bi 2 O 2 Te films (under 0.07 µW cm −2 at 210 nm), [7] showed significant photoresponse characteristics when these UV devices detect weak signals, and can provide inspiration for future work. Therefore, it is of great significance to realize weak light detection in the UV region.In recent years, the organic-inorganic hybrid perovskites offer great possibilities for optoelectronic applications, due to their long carrier lifetime, high carrier mobility, solution accessibility, and low device fabricated cost. [8] As a powerful complement to hybrid perovskites, 2D layered perovskites break the restriction of tolerance factor on cations and exhibit strong structural tunability and compatibility. [9] The alternation of the inorganic and organic layers naturally forms the quantum-well structure, which shows the excellent semiconductor properties such as strong UV absorption, and lays the foundation for efficient UV photodetection. [10] The detection limit of photodetectors can be reduced by improving crystal quality, restraining dark current, and improving carrier transport efficiency. [11] In addition, highquality bulk crystals grown by a "green" solution method are not only ideal candidates for the assembly optoelectronic device, but also restrain the trap density and reduce dark current for more sensitive photodetection. [12] Therefore, it is highly desirable to fabricate UV photodetectors with low detection limit using high-quality 2D hybrid perovskites bulk single crystals.Herein, grown via a temperature-cooling method, we obtained an inch-scale crystal of 2D organic-inorganic perovskite (BA) 2 PbBr 4 (1, BA = C 4 H 9 NH 3
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